The invention relates to gasket valve assemblies that are adapted to be mounted to trucks containing fluid. Specifically, the present invention is particularly advantageous for milk trucks (where milk and milk products are herein referred to as xe2x80x9cproductxe2x80x9d). In particular, the present invention relates to a system for allowing airflow to occur between ambient air and the interior portion of a tank. Further, the present invention is advantageous for addressing pressure surge.
In the dairy industry, milk is commonly transported from dairy farms to a central processing center by means of tank trucks and trailers. The milk-containing tank itself is generally made of stainless steel and is commonly of a double-walled construction with insulation between the inner and outer stainless steel walls, so that the contained milk can be kept at an adequately low temperature while being transported.
Because of the sanitation requirements of the dairy industry, the interior of the milk tank must be thoroughly washed at regular intervals. Also, it is necessary to provide the tank with an access opening, commonly called a xe2x80x9cmanholexe2x80x9d, to permit an inspector to actually enter the interior of the tank. Obviously, while milk is being transported, this access opening must be properly covered both to prevent milk from being spilled out of the opening, and also to prevent outside contaminants from being mixed with the milk. There is a further requirement that the interior of the tank be vented to the outside atmosphere, since with an airtight tank even small temperature variations in the milk would cause undesired pressure differentials between the area inside the tank and the surrounding atmosphere.
A quite common means of providing the venting in a milk tank is to provide a venting member in an interior metal cover which normally closes the access opening of the tank. This venting member generally comprises a cylindrical tube mounted to the center of the cover and extending downwardly toward the interior of the tank. The interior of the tube is provided with a set of vertically spaced, staggered baffles which overlap sufficiently to define a circuitous passageway from the interior to the exterior of the tank. An annular gasket member made of a flexible material is usually placed between the perimeter portion of the cover and the support ring which defines the tank access opening, to provide a perimeter seal. Also, an exterior dust cover is positioned over the interior cover. The sanitation standards of the dairy industry require that all components which possibly come into contact with the milk be thoroughly cleaned at regular intervals.
While the prior art disclosure assembly described above has been able to perform the closing and venting functions for a milk tank in a manner to meet the standards of the dairy industry, there was a continuing need for improvement. Accordingly, there was conceived another venting closure arrangement for a milk tank, and various embodiments of this are disclosed in U.S. Pat. No. 4,081,107, issued Mar. 28, 1978, and U.S. Pat. No. 4,127,216 issued Nov. 28, 1978. In general, there is described in those patents a closure assembly where there is a venting closure member having perimeter flange members which fit against a support ring of the milk tank to form a circumferential seal and one or more circumferential venting channels. There is an outer cover having a vent opening which fits over the closure member and engages the peripheral portion thereof to form the circumferential seal against the support ring. The venting channel or channels connect to circumferentially spaced openings in the flanges to provide venting from inside the tank to the area outside the tank, while preventing both spilling of the milk and contamination from outside sources.
While the assembly described in the immediately preceding paragraph is believed to be a substantial improvement over the earlier closure assembly described above, and while this improved assembly in general has been found to function quite well in accomplishing its intended functions, it has been found that under certain circumstances it is possible for liquid in the containing chamber to pass out through the circumferential venting channel.
The main inner plate portion has an upper surface that is frusta-conical and slopes downwardly when traveling radially outwardly. The surface is at a desirable angle so the product that reaches the flow area will travel radially outwardly. This radial sloping of surface prevents product from pooling on the main inner plate portion. Product that is caught on the upper surface of the main inner plate portion can rise in temperature, which causes the product to spoil after a short manner of time. When a new surge of product is rushed to the flow area the spoiled product will then flow back into the main tank compartment.
Another advantage of having an angled plate is that it prevents product from being thrusted vertically out of the tank through the outside venting due to vibrations. When a milk truck travels the main inner plate portion vibrates. If product is trapped in the central portion this causes the droplets of the product to bounce out of the first outside venting structure. This splattering of product outside of the milk tank can be disruptive to other motorist.
Accordingly, it is an object of the present invention to provide an improved venting closure assembly for a milk tank which performs the closure function yet more reliably, while still permitting venting of the containing structure. It is yet another object to provide such a venting closure member that is able to meet the standards of sanitation and other requirements of the dairy industry.
A closure assembly for a containing structure told liquid product where the containing structure has a containing chamber for liquid and has an opening such as a manhole that is defined by a ring structure. The outside cover member has an outer perimeter portion that can be positioned adjacent to the ring structure. The outside cover further has an inner portion that extends to the perimeter portion and the inner portion has a vent opening that leads to the ambient atmosphere. The closure member is adapted to be positioned in an operating location adjacent to the cover. The closure member has an upper surface and a center location as well as a perimeter location. The upper surface has a positive slope (i.e. slopes downwardly) from the center portion to the perimeter portion the closure member further has an inner portion with an inner perimeter where a vertical extension is located. The inner perimeter is located below the first vent opening. The closure member has a relaxed position where the inner portion is spaced hourly from the first vent opening to permit airflow through the first vent opening. The closure member has an upwardly deflected position with an upper surge exerts force upon the closure member and the vertical extension of the closure member is positioned against the first vent opening but allows communication between the containing structure and the ambient air. The closure member further has a second vent opening spaced from the first vent opening and leading to a containing chamber to allow airflow to a from the containing chamber to an area between the cover member and the closure member. The venting closure member in its operating location and in its relaxed position in the containing chamber can be vented to ambient atmosphere and with a surge force exerted on the closure member the closure member moves to its upwardly deflected partially closed position to allow moderate flow of liquid outwardly through the first vent opening.